1. Field of the Invention
The present invention relates to a sheet feeding apparatus for use in, for example, copying machines and printers for feeding sheets including recording paper.
2. Description of the Prior Art
In a copying machine equipped with a recirculating document handler (RDH) for stacking up a plurality of documents of single form thereon, for separating either an uppermost or bottommost document from the remaining stacked documents, feeding the separated document one by one, returning the document to either under the bottommost document or over the uppermost document after reading the image thereof, a sheet feeding apparatus, such as a document feeding apparatus of the above type and a sheet feeding apparatus for separating the prestacked recording paper and feeding the separated recording paper one by one, is used. Also, in various types of printers and photographing devices, a sheet feeding apparatus is used for separating the recording paper to be fed from the remaining stacked paper and feeding the separated paper one by one. In such a sheet feeding apparatus, it is required to separate the sheet to be fed from the remaining stacked sheets one by one. Accordingly, there have been known various sheet separating methods, such as the air flow separating method, separating claw method, and method for separating sheets by the use of a separating roller rotated in a direction opposite the sheet feeding direction.
"Sheet feeding apparatus" disclosed in Japanese Laid-open Patent No. 58-78932 is known as an example of the prior art incorporating the sheet separating method by the use of air flow. U.S. Pat. No. 3,198,514 and Japanese Patent Publication No. 55-19859 disclose respectively similar configurations to the one of the invention. FIG. 1 shows a side elevation of such a configuration. This configuration embodies an intermediate containing device 1 in a copying machine equipped with an RDH. In the case where document images are to be recorded to the both sides of the recording paper, recording paper sheets, to one sides of which have the document images recorded, are temporarily contained in the intermediate containing device 1 with being stacked thereon, and then the stacked sheets are separated one by one to be fed from the intermediate containing device 1 so that the other sides thereof have the images recorded thereto. The intermediate containing device 1 comprises a support tray 3 on which the recording paper sheets 2 are stacked.
At the downstream side of the feeding direction A1 of the recording paper 2 placed on the support tray 3 and in the periphery of the widthwise center of the support tray 3 intersecting with the feeding direction A1 is formed a notch 4. Under the support tray 3 is disposed a feed belt 7 having many penetration holes formed thereon with stretched on a pair of rotating rollers 5, 6 disposed with spaced to each other. The feed belt 7 is exposed at the notch 4. Between the rollers 5, 6 is disposed an air intake duct 8 facing the notch 4 through the feed belt 7. The recording paper 2 on the support tray 3 is vacuum attracted to the feed belt 7 by the air intake duct 8 and fed in the feeding direction A1 by drivingly moving the feed belt 7. On the other hand, there is a possibility that a plurality of the recording papers 2 on the support tray 3 are vacuum attracted to the feed belt 7 at the same time and thereby fed together. In order to obviate such a possibility, above the downstream side of the support tray 3 with respect to the feeding direction A1 are arranged an air injection duct 9 and a plurality of nozzles 10 parallel to the feeding direction A1, the nozzles communicating to each other.
The air injection duct 9 and the support tray 3 of this prior art are arranged as shown in FIG. 1. The nozzles 10 directs the flat air flow of a constant quantity concentratedly to the fixed position in the periphery of the downstream end of the support tray 3 with respect to the feeding direction A1. Thereby, the recording papers 2 stacked on the support tray 3 are effectively separated. Accordingly, assuming a case where relatively large-sized recording papers 2 are used, the constant quantity of the air blown from the nozzles 10 requires to be relatively large. In this case, when the relatively small-sized recording papers 2 are fed, there is a likelihood that such excessive air flow may flap the recording papers 2. On the contrary, assuming a case where relatively small-sized recording paper sheets are used, the constant quantity of the air blown from the nozzles 10 requires to be relatively small. In this case, when the relatively large-sized recording papers 2 are fed, the recording papers 2 cannot be effectively separated, thereby causing troubles such as multiple feeding and poor feeding of the sheets. Similarly, problems as mentioned above occur in the cases where relatively large number of the recording papers 2 or relatively small number of the recording papers 2 are contained in the intermediate containing device 1.
In order to overcome such problems, the quantity of the air flow from the nozzles 10 requires to vary, which feature is incorporated in such prior arts in which the rotating speed of a fan for e.g. separating the air flow is changed. However, such prior arts requires to have a special circuit for changing the rotating speed of the fan and a complicated software for driving such circuit, resulting in a complicated construction.
In the case where the recording paper sheets used therein are limited to the predetermined types or quantities, the prior arts demonstrate the relatively satisfactory capability of separating the sheets. However, in terms of versatility of effectively separating the recording paper sheets in a wide variety of sizes or quantities, the prior arts do not demonstrate sufficient versatility since they are liable to meet a sheet separation failure or feeding failure. Accordingly, a sheet feeding apparatus is desired which has capability of effectively separating the recording paper sheets in a wide range of sizes and quantities.